you really can use wordpress to build apps

[Costas]

ref - https://torquemag.io/2014/06/yes-you-really-can-use-wordpress-to-build-apps/

Twig - The flexible, fast, and secure template engine for PHP - http://twig.sensiolabs.org/
handlebars - js template engine - http://handlebarsjs.com/
wp lib - PHP Library that Adds Modules and Applications to WordPress - https://github.com/wplib/wplib
WP MVC - MVC framework for WordPress - https://github.com/tombenner/wp-mvc
Custom Field Suite - custom fields management UI - https://wordpress.org/plugins/custom-field-suite/